Reaction of the transient species W(CO)(5)(cyclohexane) with cyclo-C4HnO (n=4, 6, 8) studied by time-resolved infrared absorption spectroscopy

Citation
A. Lugovskoy et al., Reaction of the transient species W(CO)(5)(cyclohexane) with cyclo-C4HnO (n=4, 6, 8) studied by time-resolved infrared absorption spectroscopy, J PHYS CH A, 104(45), 2000, pp. 10587-10593
Citations number
45
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF PHYSICAL CHEMISTRY A
ISSN journal
1089-5639 → ACNP
Volume
104
Issue
45
Year of publication
2000
Pages
10587 - 10593
Database
ISI
SICI code
1089-5639(20001116)104:45<10587:ROTTSW>2.0.ZU;2-#
Abstract
Time- and temperature-resolved infrared absorption spectroscopy is used to monitor the ligand substitution reaction of W(CO)(5)(cyclohexane) with a se ries of ligands L of the form cyclo-C4HnO (n = 4, 6, 8). Second-order rate constants for the formation of W(CO)(5)(L) are obtained over the temperatur e range 20-60 degreesC, and from these temperature-dependent rare constants , activation parameters for the ligand substitution reaction are obtained. We find that for L = furan, DeltaH(double dagger) = 7.1 +/- 0.7 kcal mol(-1 ) and DeltaS(double dagger) = -7.1 +/- 5.1 eu; for L = 2,3-dihydrofuran, De ltaH(double dagger) = 5.9 +/- 0.5 kcal mol(-1) and DeltaS(double dagger) = -8.9 +/- 7.3 eu; and for L = 2,5-dihydrofuran, DeltaH(double dagger) = 3.8 +/- 0.2 kcal mol(-1) and DeltaS(double dagger) = -14.0 +/- 3.5 e.u. We find that as L becomes less strongly electron-donating, as determined by the tr ans C-O stretching force constant of W(CO)(5)L, DeltaH(double dagger) rises and DeltaS(double dagger) becomes less negative. The correlation of the ac tivation enthalpy with the properties of the products and the low activatio n enthalpies relative to the (CO)(5)W-cyclohexane bond dissociation energy are consistent with an associative interchange (I-a) mechanism for the liga nd exchange.